Machines of the piston-pump type



Oct. 29, 19 63 V 7 PEANHARD MACHINES OF THE PISTON-PUMP TYPE Filed July 18, 1961 4 Sheets-Sheet 1 1963 1 P. PANHARD 3,108,436

MACHINES OF THE PISTON-PUMP TYPE Filed July 18, 1961 4 Sheets-Sheet 2 Q l l l I m :a 1; 3% 8% I 1 Nu. 1 mm 3 i H N i l l [11]] I g fi'! Lil a INVENTQR BY I ATTORNEY Oct. 29, 1963 P. PANHARD A I 3,103,436 MACHINES OF THE PISTON-PUMP TYPE y Filed July 18, 1961 4 Sheets-Sheet 3 ATTORNEY Oct. 29, 1963 P. PANHARD MACHINES OF THE PISTON-PUMP TYPE Fiied July 18, v1961 4 Sheets-Sheet 4 w mm MM new MN mm INVEN TOR ATTORNEY United States Patent 3,198,436 MACHENES ill Tl-E PlSTGtN-PUMP TYPE Paul Panhard, Paris, France, assignor to Societe. Anonyme ties Anciens Etablissements Pant-hard & Levassor, Paris,

Seine, France, a society of France Filed .luly 18, 196i, Ser. No. 124,868 Claims priority, appiication France July 19, 1960 4 Claims. (Cl. 60-52) The present invention relates to machines of the piston-pump type, and, since its application appears to offer the greatest advantage in their case, it is more particularly but not exclusively concerned with hydraulic energy generating machines which are coupled in hydraulic transmissions to receiving machines, that is to say to machines adapted to transform the said hydraulic energy to mechanical energy.

In hydraulic transmissions and other installations, it is important that the generating machine should have an output which remains as constant as possible during the course of each cycle of operation of the machine, all other things being equal. This so-called homokinetic condition is diihcuit to satisfy in practice with generator machines having alternating pistons, and to this end, machines of this kind have up to the present time been provided with at least six cylinders arranged in line, in star or in barrel, which complicates the construction of the machine and also its valve-gear mechanism at suction and at delivery.

In addition, in order to be able to vary the ratio of a hydraulic transmission of this kind, the latter generally comprises a mechanism by which the output of the generator machine may be regulated by acting on the travel of the pistons of the machine. Up to the present time, such a mechanism acted on the travel simultaneously towards the inner dead centre (LDC) and towards the outer dead centre (O.D.C.), so that the dead space existing at the LDC. between each piston of the generator machine and the corresponding cylinder varied inversely with the amplitude of the stroke and reached its maximum in the vicinity of zero output, that is to say in general in the vicinity of the maximum delivery pressure.

Now, in the hydraulic transmissions of automobile vehicles for example, this maximum pressure is high enough to cause on the one hand a not'negligible compression of the hydraulic liquid, and on the other hand an appreciable expansion of the walls of the cylinder, these two phenomena resulting conjoint-1y in a loss of energy which may attain 20%.

The invention has for its object to make the abovementioned piston-pumps comply better with the various requirements of practice than has heretofore been the case.

The invention mainly consists, with a view to obtaining homokinetic machines of the kind in question, in providing them solely with two groups each comprising a cylinder and a piston, and in driving the machine by means such that the delivery periods of one group coincide substantially with the suction periods of the other group and vice versa, the delivery periods being however longer than the suction periods, so that the beginning of the delivery period of each group is super-imposed, for a certain space of time, on the end of the delivery period of the other group, the above-mentioned means being furthermore such that the sum of the relative speeds of the two pistons with respect to the corresponding cylinder, during each of the above spaces of time, is constant and equal to the relative speed, also constant, of each piston during that portion of its delivery period which is outside the said spaces of time.

hitidA-Eh Apart from this main arrangement, the invention cornprises certain other arrangements which are preferably employed at the same time, but which could be used separately when so desired, and which will be referred to in more detail below, and especially a second arrangement which, while utilizing machines of the kind in question as generator machines of a hydraulic transmission and in providing them with a mechanism for varying the amplitude of the stroke of their pistons, in arranging this mechanism in such manner that, irrespective of the value which it gives to this amplitude, it always brings each piston back to the same inner dead centre, while always maintaining at its minimum value the dead space included between the piston and cylinder corresponding to this I.D.C.

The invention is more particularly directed to a certain form of application to hydraulic transmission, especially for automobile vehicles, and also to certain forms of embodiment of the said arrangements, and it is still more particularly directed, by way of new industrial products, to machines of the kind in question to which these same arrangements are applied, the special elements proper to their establishment, and also the units such as hydraulic transmissions comprising similar machines or transmissions.

The invention will be more clearly understood by means of the further description which follows below, together with the accompanying drawings, the said description and drawings being understood to be given especially by way of indication.

FIGS. 1, 2 and 3 of the drawings show respectively in elevation with parts cut away and in cross-section along the line 11-11 and 1Il-III of FIG. 1, a generator machine of a hydraulic transmission in accordance win the invention.

FIG. 4 shows a diagrammatic arrangement similar to FIG. 1 of the mechanism which serves to regulate the amplitude of the stroke of each piston.

FIG. 5 shows curves illustrating the operation of the same machine.

Finally, FIGS. 6 to 9 illustrate the operation of the distribution and reversing mechanism shown in FIG. 2.

In accordance with the invention, and more particularly according to that method of application and those forms of construction of its vmious parts to which preference is given, a generator machine for a hydraulic transmission is established in the followin way.

This machine is provided solely with two groups, each formed by a cylinder 1 or 2 and a piston 3 or 4 (FIG. 2), and it is driven from a shaft 5, preferably actuated by an internal combustion engine (not shown), by means such that the periods of delivery of one group (upward movement in FIG. 2 of the corresponding piston 3 or 4) coincide substantially with the suction periods of the other group (downward movement of the other piston) and vice versa, while the delivery periods are slightly longer than the suction periods, so that the beginning of the delivery period of each group is superposed, during a certain space of time, on the end of the delivery period of the other group, the said means being fur-thermore such that the sum of the relative speeds of the two pistons 3 or 4 with respect to the corresponding cylinder 1 or 2, during each of the above spaces of time, is constant and equal to the relative speed (also constant) of each piston during the portion of its delivery period which is situated outside the said spaces of time.

in general, the two cylinders 1 and 2 are carried by a stationary unit 6 and the pistons 3 and 4 are displaced in their respective cylinders by a rotary cam. In the most frequent case, in which the said cam has a single boss,

that is to say Where it is obliged to turn through 360 to cause a to-and-fro movement of the corresponding piston, the above-mentioned condition is obtained by causing the portion of the cam which determines the delivery stroke of the corresponding piston to extend over more than 180, with the obvious result that the portion of the cam determining the suction stroke extends over less than 180. It is also clear that if the cam has a number n of bosses equal to or greater than 2, it would be necessary to replace 180 in the foregoing phrase by 180/n.

According to the form of embodiment shown, the two pistons 3 and 4 are respectively driven by two fiat cams 7 and 8 which are keyed on the same shaft 9 and which act at their periphery, through the intermediary of rocker-arms 1t) and 11, on the rods 12 and 13 of the pistons, the thrust applied by each cam on the rocker-arm determining the delivery stroke. in this case, each cam is given a positive lift profile extending over an arc in the vicinity of 210 (shown in FIG. 1 for the cam 8) and formed by a central portion with an Archimedean spiral comprised between two end coupling portions. The radius of this spiral measured from the axis of the shaft 9, as seen by a stationary observer, is such that when the cam rotates in its normal direction of operation indicated by the arrow 1 in FIG. 1, the said radius increases linearly as a function of the angle of rotation of the cam.

Although it is possible to arrange the cylinders 1 and 2 differently, these two cylinders are advantageously disposed in line, in which case the profiles of the two cams 7 and 8 may be deducted one from the other by rotation through 180 about the axis of their common shaft 9.

The form of the profile of the two cams is shown at the bottom of FIG. 5, on which have been drawn in abscissae the angular position 06 of the shaft 9 and in ordinates the lift L of the cams, the curve L in full lines relating to the cam 7 and the curve L in chain-dotted lines, the cam 3. There have been indicated by A the positive lift profiles of the two cams 7 and 8, the Archimedean spiral portions of the cams 7 land 8 corresponding respectively to the straight rising portions of the curves L and L2.

At the top of FIG. 5, on which have been drawn with the same abscissae as at the bottom of the figure, the linear speeds V of the pistons as ordinates, the curves V in full line and V in chain-dotted lines correspond to the similar curves at the bottom of the figure, that is to say to the pistons 3 and 4 respectively. The portions of these curves which are located above the axis 006 (positive speeds) correspond to the deiivery strokes, and the portions located below the said axis to the suction strokes.

It can be seen that the piston 3 delivers alone at a constant speed V during the rotation of the shaft 9 through the angle a (equal to about 150), that the piston 4 delivers alone at the same constant speed V during rotation through the angle b (equal to the angle a) and that through the residual angles c, the two pistons deliver together at variable speeds, the sum of which (kl=km+kn) is however equal to the above-mentioned value V The value of this sum is indicated by a heavy line at the top of FIG. 5. It should be noted that A=a+2c=b+2c. The homokinetic condition is therefore fulfilled at the delivery of the generator machine, and its output can be applied to the receiving machine 14 of a hydraulic transmission through the intermediary of one of two conduits 15 and 16, the other of which serves for the return of the hydraulic liquid, without any shocks being produced in the transmission.

While the homokinetic condition is fully obtained at the delivery of the pump, it is not obtained at the suction, as can be seen from examination of the sections of the curves V and V at the top of FIG. 5, which are located below the axis Oz.

in particular, each time the two pistons 3 and 4 discharge simultaneously (space of time corresponding to the angles 0), it is clear that they cannot receive the liquid discharged at constant rate of flow from the receiver machine 14, and it is therefore necessary to provide between the latter and the generator :machine a system adapted to compensate for the periodic variations of the flow at the suction of this machine.

To this end, the receiver machine could be coupled to a tank maintained at atmospheric pressure and the suction of the generator machine could be coupled to this tank. It is also possible to connect on the piping 15 or 16 which communicates with the said suction, an expansion chamber containing a compressible fluid (nitrogen for example), preferably isolated by a moving or elastic fluid-tight wvall. However, it appears more advantageous to associate with the main cylinders and pistons described above a compensating cylinder 17 and a piston 18, the cylinder 17 communicating continuously with the return conduit 15 or 16, and the piston 18 being driven in synchronism with the main pistons 3 and 4 from the shaft 9.

In order to actuate the piston 18, it is an advantage to key on the shaft 9 a third cam 19 which acts through the intermediary of a rocker-arm 20, on the rod 21 of the piston 18. The profile of the cam 19 is shown in FIG. 5, which has been drawn with the assumption that the cylinders 1, 2 and 17 have the same bore and that the rockerarms 10, 11 and 20 have the same lever-arm effect. In this drawing, the curves L and V in broken lines correspond to the said cam 19.

If the sign is given to the speeds vw and we of the main pistons and vy to the speed of the compensating piston during the delivery strokes (above the line Out at the top of FIG. 5) and the sign being given to the suction strokes, the speed vy of the compensating piston 13 in algebraic value should be equal and opposite to the sum of the speeds vw+vx of the main pistons 3 and 4 (in algebraic value). The cross-hatched symmetrical zones in FIG. 5 correspond to volumes delivered by one of the main pistons and sucked-in by the compensating piston, which balance each other exactly.

Naturally, if the bore of the compensating cylinder were different from those of the main cylinders 1 and 2, it would be necessary to take this into account by associating proportionality coefficients with the linear speeds It can be seen from the bottom of FIG. 5, that the cam 19 should have a profile having two rectangular axes of symmetry, which is confirmed by FIG. 1.

The essential advantage of the presence of two pumping pistons 3 and 4 only, resides in the considerable simplification which can be made to its distributor system. In fact, whereas with a generator machine having more than two pistons, it is necessary to have recourse to at least one rotary distributor device of complicated shape, the invention permits the use of a single alternating distributor advantageously constituted by a slide-valve 22.

A slide-valve of this kind is preferably provided with two bearing surfaces 22a and 2212 which, inside a bore 23, on the one hand de-limit between each other a central chamber 24, and on the other hand a side chamber 25 or 26 on each side. Ports 27, 28, 29, 3t), 31 and 32 open into the length of the bore 23, the said ports communieating respectively with the cylinder 1, the cylinder 2, the cylinder 17 (through the intermediary of a conduit 33), that of the two conduits 15 and 16 which serves for the delivery, and the other of the conduits 15 and 1.6 (for the two ports 31 and 32). The chambers 24, 25 and 26 communicate continuously with the ports 30, 31 and 32 respectively.

Depending on whether the slide-valve 22 is at the right or the left-hand side of FIG. 2 and FIGS. 6 to 9, the cylinder 1 is put to suction by the port 27, the chamber 25 and the port 31, and the cylinder 2 is put to delivery by the port 28, the chamber 24 and the port 30 (FIGS. 2, 6 and 8), or alternatively the cylinder 1 is put to delivery by the port 27, the chamber 24 and the port 30 and the aioaase cylinder 2 is put to suction by the port 28, the chamber 26 and the port 32 (FIGS. 7 and 9).

In the intermediate periods in which the two pistons 3 and 4 deliver simultaneously, the distributor 22 occupies its central position for which the cylinders 1 and 2 both communicate with the chamber 24 and in consequence with the port In all cases, the cylinder 17 communicates with the suction conduit or 16 by the channel 33, the chamber 26 and the port 32.

In order to actuate the slide-valve 22, any kind of mechanism can be employed which derives its motion from the shaft 5, in particular on the camshaft 9. There is however an advantage in utilizing for this purpose an oscillating lever 34 fixed to a ring 35 which is mounted through the intermediary of an oblique bearing surface 36 (PEG. 3) on the shaft 9, balls 37 being preferably interposed be ween the bearing surface 36 and the internal surface of the ring 35. The extremity of the lever 9 opposite to the ring 35 engages the rod 39 of the slidevalve 22 through the intermediary of a knuckle-joint 38. In this way, each revolution of the shaft 9 gives the desired reciprocating motion to the slide-valve 22.

When the hydraulic transmission is required to permit a reversal of the direction of running of the receiver machine 14, which is especially the case with vehicle transmission, there is associated with the distributor slide-valve 22 a device adapted to change-over the connections between the delivery chamber 24 and the suction chambers 25 and 26 on the one hand, and the conduits 15 and 1.6 on the other. For this purpose, use is preferably made of a slide 40 housed in a bore 41, in which it defines, by virtue of two bearing surfaces 4% and 4%, a central chamber 42 and two lateral chambers 43 and 44, the slide 4% having in addition a central passage or cavity which puts the lateral chambers 43 and 44- coutinuously in communication. The central chamber 42 communicates continuously with the delivery port 30 and the lateral chambers 43 and 44 with the suction ports 31 and 32 respectively.

If the slide 49 is pushed towards the left of FIGS. 2 and 6 to 9, for example by means of a manual control as, the chamber 32 communicates with the conduit 15 which thus becomes the delivery conduit, and the chamber id with the conduit 16 which thus becomes the suction conduit (FIGS. 6 and 7). If the slide is pushed towards the right of the said figures, the chamber 42 communicates with the conduit 16, which thus becomes the delivery conduit, and the chamber 43 with the conduit 15 which then becomes the suction conduit (FIGS. 2, 8 and 9).

In order to permit the transmission ratio between the generator machine and the receiver machine 15 to be varied, the generator machine is provided with a mechanism permitting of the simultaneous variation in the same ratio, the amplitude of the stroke of the main pistons 3 and 4 and the compensating piston 1%.

To this end, these pistons being actuated by cams 7, 8 and w, keyed on the same shaft 9, through the intermediary of rocker-arms it 11 and 29, the axes of rotation of these rocker arms are aligned, the cams are caused to act on these rocker-arms in a single plane PP parallel to the plane QQ passing through the axes of the cylinders l, 2 and 17, preferably through the intermediary of rollers such as 47, fixed to a guiding member 47a parallel to the said planes, and the above-mentioned mechanism is arranged in such manner that it moves simultaneously, while keeping them in line, the axes of rotation of the rocker-arms perpendicular to their common direction.

In accordance with a particularly advantageous arrangement of the invention and which may furthermore be employed more generally on generator machines having any desired number of pistons for hydraulic transmission, the said mechanism is arran ed so that, irrespective of value which it gives to the amplitude of the stroke of the main pistons 3 and 4, it causes each of these pistons to return always to the same inner dead centre (or top dead centre if FIG. 2 is considered), While maintaining always at its minimum value the dead space comprised between the piston 3 or 4 and the corresponding cylinder 1 or 2.

if there is designated by X the position of the pivotal axis of the pistons on the rocker-arms at the inner dead centre which is desired to be invariable, by Y the position of the pivotal axis on the rocker-arm of the crank of variable length which is equivalent to the coupling by the cam 7 or S and roller 37, and by Z the common pivotal axis of the rocker-arms on the frame 6 (FIG. 4), in order that the pistons shall always reach the same inner dead centre, it is only necessary for the above-mentioned mechanism to displace the axis Z in the plane passing through the axes X and Y. According to the form of embodiment shown, the axis Y coincides with the axis of the roller 47.

In FIG. 4 there is shown in full lines, for a given position of the axis Z, the position of one of the rocker arms it: and ill of one of the pistons 3 and 4 at its I.D.C. (which it is desired to make invariable), of the roller 47 corresponding to its lowest point (invariable by construction), and of the trajectory 48 of the axis Z which is invariably coupled to the rocker-arm considered. There has been shown in chain-dotted lines the position of the same elements (with the exception of the rocker-arms) for the same position of the axis Z, but when the piston 3 or 4 is at its outer dead centre. Finally, there has been shown in broken lines the position taken by the trajectory 43 coupled to the rocker-arm, when the axis Z is brought into coincidence with the axis X (the case of FIG. 1), in which case the rocker-arm oscillates about the said axis X and maintains the piston 3 or 4 constantly in its position of full lines (zero output). In any case, it will be understood that the piston always returns to the same inner dead centre (full line position in FIG. 4) irrespective of the position of the axis Z on its trajectory 48, and that in consequence the dead space is always maintained at the same minimum value.

in order to materialize the axis Z, use has advantageously been made of bearing bushes 49, 5t), 51 which have a circular arcuate bearing surface coaxial with the said axis Z and on which are supported segments such as 52 which are themselves provided with a flat bearing surface on which is supported a transverse rib embodying the trajectory S8, rolling needles being preferably provided between the bearing bushes and segments and between segments and ribs, as can be seen in FIGS. 1 and 2.

In order to materialize the axis X, a similar arrangement is employed, the piston rods 12, 13 or 21 having a circular arcuate bearing surface coaxial with the axis X, in which is housed a segment such as 53, the flat portion of this segment being supported on the rib 48. A nipple such as 54, projecting from the segment 53 into an opening provided on the rocker-arm i1 and more particularly in its web, prevents this rocker-arm from being displaced longitudinally.

The bearing bushes 49, S9 and 51 are conjugated for example by a transverse shaft 55 carrying teeth 56 with which are engaged the racks 57 rigidly fixed to the said bearing bushes. The bushes are preferably actuated by a hydraulic control which may comprise a moving cylinder 53 or 59 capable of sliding on a fixed piston such as 60, piping systems 61 enabling oil to be admitted under pressure at will to the right-hand or left-hand side of the piston es of the corresponding cylinder. It is generally only necessary to provide one such cylinder for each of the main pistons 3 and 4. As shown in the drawing, the racks 5'7 may be formed directly on these cylinders.

By this arrangement, there is obtained a hydraulic transmission, the operation of which is as follows:

When the shaft 5 is driven by the motor, the pistons 3 and 4 deliver at a uniform flow to the receiver machine, either separately or conjointly, as shown by the horizontal line V at the top of FIG. 5. In the same way, the unit constituted by the cylinders 1 and 2 and the compensating cylinder 17 absorbs the uniform flow derived from the machine 14, as shown by the horizontal line V in the same figure. Depending on the position given to the slide 40, the machine 14 can thus be driven without jerks either in one direction or in the other. In addition, according to the position given to the bearing bushes 49, d, 51, it is possible to act on the output of the generator machine and in consequence on the ratio of transmission.

The advantages of a transmission of this kind are especially as follows. The alternating distributor of slidevalve 22 which can be adopted by virtue of the presence of only two alternating pumping sets, keeps open to the maximum degree and for the maximum time, the passages connecting the cylinders 1 and 2 to the conduits and 16. In addition, such a distributor is balanced and therefore only requires very small driving forces and is practically not subject to leakage.

The compensating piston 13 with a positive drive enables the engine, coupled to the shaft 5, to be started-up by acting on the output shaft of the machine 14, which is of particular advantage in the case of transmissions for vehicles, irrespective of the stroke imposed on the pumping pistons 3 and 4 (with the obvious condition that they are diiferent from zero) by reason of the conjugation by toothed racks between the bearing bushes 4?, 5th and 51.

As the dead space is always a minimum at the LDC. of the pumping pistons, the losses of energy remain small, even when the strokes of these pistons are short.

Finally, the construction of the sliding direction reverser enables a complete fluid-tightness to be obtained without wear and ensures a smooth, uniform circulation of oil.

It will of course be understood from the foregoing description that the invention is furthermore not in any way limited to that form of application or to the forms of embodiment of its various parts which have been more particularly considered; on the contrary, it embraces all the alternative forms.

What I claim is:

1. A hydraulic transmission system which comprises, in combination, a pump, a receiver machine, a pump delivery conduit leading from said pump to said receiver machine, and a pump suction conduit leading from said receiver machine to said pump, said pump including a frame, only two single-acting pum ing groups mounted in said frame and similar to each other, said two groups being identical and each of them comprising a cylinder, a piston slidable in said cylinder with a liquidtight fit so as to form therewith a variable volume working chamber, a shaft, and driving means, operatively connected with said shaft for reciprocating each of said pistons in its cylinder respectively, with an offsetting of 180 of said pistons with respect to each other, the displacements of each of said pistons in the directions that reduce the corresponding working chamber being called delivery strokes, and the displacements in the opposed directions suction strokes, said driving means being arranged to give each of said pistons a constant speed equal to a given value during an intermediate portion of every delivery stroke thereof, said driving means being adapted so that the angle of rotation of said shaft corresponding to a delivery stroke of each of said pistons is greater than, and overlaps at both ends, that corresponding to a suction stroke of said last mentioned piston, whereby each of said pistons must have, during an intermediate portion of each of its suction strokes, a speed higher than said constant speed, said suction stroke portion being called high speed suction stroke portion, whereby, at the beginning and at the end of every delivery storke of each said pistons, there is a period for which the other piston is also moving in the delivery stroke direction, said driving means being adapted to give said pistons, during said periods, respective speeds having a sum equal to said given value, and a single moving valve member in said frame for connecting each of said working chambers with said delivery conduit during every delivery stroke of the corresponding piston and with said suction conduit during every suction stroke of said last mentioned piston, a third cylinder mounted in same frame, a third piston slidable in said third cylinder with a liquidtight fit so as to form therewith a third woridng chamber, the movements of said third piston that reduce the volume of said third working chamber being called delivery strokes and the movements of the same piston that increase the volume of said third working chamber being called suction strokes, third driving means for reciprocating said third piston in said third cylinder, said third driving means being operatively connected with said first mentioned driving means to move said third piston on its delivery strokes during the high speed suction stroke portions of the two first mentioned pistons and to move said third piston on its suction strokes during the time intervals between said delivery strokes, means for connecting said third working chamber constantly with said suction conduit and means operative by said single valve member for connecting said third working chamber, during every delivery stroke of said third piston, with that of the two first mentioned working chambers where the corresponding piston is moving on its suction stroke.

2. A hydraulic transmission system according to claim 1 further comprising a reversing valve system interposed between said delivery and suction conduits and said valve means.

3. A hydraulic transmission system according to claim 2 further comprising means for varying the lengths of stroke of said pistons and means for keeping the inner dead center positions of said pistons in the same position with respect to their cylinders, respectively, irrespective of the variations of their lengths of stroke.

4. A hydraulic transmission system which comprises, in combination, a pump, a receiver machine, a pump delivery conduit leading from said pump to said receiver machine, and a pump suction conduit leading from said 'eceiver machine to said pump, said pump including a frame, only two single-acting pumping groups mounted in said frame and similar to each other, said two groups being identical and each of them comprising a cylinder, and a piston slidable in said cylinder with a liquidtight fit so as to form therewith a variable volume working chamber, a shaft, and two cams, both mounted on said shaft and each operatively connected with one of said pistons respectively for reciprocating it in its cylinder, with an otfseting of of said cams with respect to each other, the 'dispiacements of each of said pistons in the direct-ions that reduce the corresponding working chamber being called delivery strokes, and the displacements in the opposed directions suction strokes, said cams being shaped to give each of said pistons 21. constant speed equal to a given value during an intermediate portion of every delivery stroke thereof, said cams being shaped so that the angle of rotation of said shaft corresponding to a deiivery stroke of each of said pistons is greater than, and overlaps at both ends, that corresponding to a suction stroke of said last mentioned piston, whereby each of said pistons must have, during an intermediate portion of each of its suction strokes, a speed higher than said constant speed, said suction stroke portion being called high speed suction stroke portion, whereby, at the beginning and at the end of every delivery stroke of each said pistons, there is a period for which the other piston is also moving in the delivery stroke direction, said cams being adapted to give said pistons, during said periods, respective speeds having a sum equal to said given value, and a single slide valve member in said frame for connecting each of said working chambers with said delivery conduit during every delivery stroke of the corresponding piston and with said suction conduit during every suction stroke of said last mentioned piston, a third cylinder mounted in same frame, a third piston slidable in said third cylinder with a liquidtight fit so as to form therewith a third working chamber, the movements of said third piston that reduce the volume of said third working chamber being called delivery strokes and the movements of the same piston that increase the volume of said third working chamber being called suction strokes, a third cam for reciprocating said third piston in said third cylinder, said third cam being mounted on said shaft, to move said third piston on its delivery strokes during the high speed suction stroke portions of the two first mentioned pistons and to move said third piston on its suction strokes during the time intervals between said delivery strokes, means for connecting said third working chamber constantly with said suction conduit and means operative by said single valve member for connecting said third working chamber, during every delivery stroke of said third piston, With that of the two first mentioned working chambers where the corresponding piston is moving on its suction stroke.

References {lit-ed in the file of this patent UNITED STATES PATENTS FOREIGN PATENTS Germany Mar. 11, Great Britain July 11, Great Britain Dec. 5, Finland Dec. 7, France Sept. 30, Italy Nov. 8, 

1. A HYDRAULIC TRANSMISSION SYSTEM WHICH COMPRISES, IN COMBINATION, A PUMP, A RECEIVER MACHINE, A PUMP DELIVERY CONDUIT LEADING FROM SAID PUMP OF SAID RECEIVER MACHINE AND A PUMP SUCTION CONDUIT LEADING FROM SAID RECEIVER MACHINE TO SAID PUMP, SAID PUMP INCLUDING A FRAME, ONLY TWO SINGLE-ACTING PUMPING GROUPS MOUNTED IN SAID FRAME AND SIMILAR TO EACH OTHER, SAID TWO GROUPS BEING IDENTICAL AND EACH OF THEM COMPRISING A CYLINDER, A PISTON SLIDABLE IN SAID CYLINDER WITH A LIQUIDTIGHT FIT SO AS TO FORM THEREWITH A VARIABLE VOLUME WORKING CHAMBER, A SHAFT, AND DRIVING MEANS, OPERATIVELY CONNECTED WITH SAID SHAFT FOR RECIPROCATING EACH OF SAID PISTONS IN ITS CYLINDER RESPECTIVELY, WITH AN OFFSETTING OF 180* OF SAID PISTONS WITH RESPECT TO EACH OTHER, THE DISPLACEMENT OF EACH OF SAID PISTONS IN THE DIRECTIONS THAT REDUCE THE CORRESPONDING WORKING CHAMBER BEING CALLED DELIVERY STROKES, AND THE DISPLACEMENTS IN THE OPPOSED DIRECTIONS SUCTION STROKES, SAID DRIVING MEANS BEING ARRANGED TO GIVE EACH OF SAID PISTONS A CONSTANT SPEED EQUAL TO A GIVEN VALUE DURING AN INTERMEDIATE PORTIONOF EVERY DELIVERY STROKE THEREOF, SAID DRIVING MEANS BEING ADAPTED SO THAT THE ANGLE OF ROTATION OF SAID SHAFT CORRESPONDING TO A DELIVERY STOKE OF EACHOF SAID PISTONS IS GREATER THAN, AND OVERLAPS A BOTH ENDS, THAT CORRESPONDING TO A SUCTION STROKE OF SAID LAST MENTIONED PISTON, WHEREBY EACH OF SAID PISTONS MUST HAVE, DURING AN INTERMEDIATE PORTION OF EACH OF ITS SUCTION STROKES, A SPEED HIGHER THAN SAID CONSTANT SPEED, SAID SUCTION STROKE PORTION BEING CALLED HIGH SPEED SUCTION STROKE PORTION, WHEREBY, AT THE BEGINNING AND AT THE END OF EVERY DELIVERY STROKE OF EACH SAID PISTONS, THERE IS A PERIOD FOR WHICH THE OTHER PISTON IS ALONG MOVING IN THE DELIVERY STROKE DIRECTION, SAID DRIVING MEANS BEING ADAPTED TO GIVE SAID PISTONS, DURING SAID PERIODS, RESPECTIVE SPEEDS HAVING A SUM EQUAL TO SAID GIVES VALUE, AND A SINGLE MOVING VALVE MEMBER IN SAID FRAME FOR CONNECTING EACH OF SAID WORKING CHAMBERS WITH SAID DELIVEY CONDUIT DURING EVERY DELIVERY STROKE OF THE CORRESPONDING PISTON AND WITH SAID SUCTION CONDUIT DURING EVERY SUCTION STROKE OF SAID LAST MENTIONED PISTON, A THIRD CYLINDER MOUNTED IN SAME FRAME, A THIRD PISTON SLIDABLE IN SAID THIRD CYLINDER WITH A LIQUIDTIGHT FIT SO AS TO FORM THEREWITH A THIRD WORKING CHAMBER, THE MOVEMENTS OF SAID THIRD PISTON THAT REDUCE THE VOLUME OF SAID THIRD WORKING CHAMBER BEING CALLED DELIVERY STROKES AND THE MOVEMENTS OF THE SAME PISTON THAT INCREASE THE VOLUME OF SAID THIRD WORKING CHMBER BEING CALLED SUCTION STROKES, THIRD DRIVING MEANS FOR RECIPROCATING SAID THIRD PISTON IN SAID THIRD CYLINDER, SAID THIRD DRIVING MEANS BEING OPERATIVELY CONNECTED WITH SAID FIRST MENTIONED DRIVING MEANS TO MOVE SAID THIRD PISTON ON ITS DELIVERY STROKES DURING THE HIGH SPEED SUCTION STROKE PORTIONS OF THE TWO FIRST MENTIONED PISTONS AND TO MOVE SAID THIRD PISTON ON ITS SUCTION STROKES DURING THE TIME INTERVALS BETWEEN SAID DELIVERY STROKES, MEANS FOR CONNECTING SAID THIRD WORKING CHAMBER CONSTANTLY WITH SAID SUCTION CONDUIT AND MEANS OPERATIVE BY SAID SINGLE VALVE MEMBER FOR CONNECTING SAID THIRD WORKING CHAMBER, DURING EVERY DELIVERY STROKE OF SAID THIRD PISTON, WITH THAT OF THE TWO FIRST MENTIONED WORKING CHAMBERS WHERE THE CORRESPONDING PISTON IS MOVING ON ITS SUCTION STROKE. 